With the rapid development of information science, higher requirements for the running speed, data storage density, power consumption and other parameters of electronic components are needed. Existing electronic components represented by integrated circuits or superlarge-scale integrated circuits only control the degree of freedom of electronic charges, and ignore the other basic quantum attribute of electron spin, resulting in that the dimension, integration, etc. of the electronic components have already substantially reached a theoretical physical limit. The quantum control for the electron spin facilitates rapid data processing, reduction of power consumption, improvement of integration and so on has already become an emerging important branch of a semiconductor physics.
The core of the quantum control for the electron spin is how to effectively control a spin orientation, spin transport and spin detection. However, in the aspect of the growth of spin electron materials, there are still difficulties such as impedance mismatch of ohmic injection of semiconductor heterojunctions, significant interface scattering, low Curie temperature of a diluted magnetic semiconductor, low quality of a tunnel injection ferromagnetic thin film, non-sharp interface, high tunneling barrier and the like (1. J. W. A. Robinson, J. D. S. Witt, M. G. Blamire, Science, 329(2010), 59; 2. K. Sato, L. Bergqvist, J. Kudrnovsky, Rev. Mod. Phys., 82(2010), 1633; 3. G. Schmidt, D. Ferrand, L. W. Molenkamp, Phys. Rev. B, 62(2000), R4790), which are basically closely related to the quality control and magnetic performance control of the materials in the growth process. In the aspect of the spin transport, the spin relaxation time and a coherence length observed at present are relatively short; the spin detection is generally carried out outside the sample preparation chamber, and the spin characteristics may be influenced by various atoms absorbed on the surface when the sample is exposed to the air. On the other hand, due to the notable difference of a magnetic material thin film of a spin semiconductor heterojunction in length, width and thickness, there is high demagnetizing field in a direction perpendicular to the thin film, so that the magnetic moment of the material is basically parallel to the plane of the thin film and different in directions, thereby not facilitating the acquisition of spin current with high polarization rate. In order to change the magnetic structure, the annealing is generally carried out in a magnetic field of thousands of Gaussian. Although this mode achieves some effects, it is difficult to fundamentally change the magnetic structure of the material by introducing the magnetic field after growth, as the lattice structure of the material mainly depends on the atomic arrangement in the preparation process. Therefore, the direct epitaxial growth of materials under strong magnetic field is beneficial to the formation of a more uniform magnetic domain structure, thus acquiring the spin current with high polarization rate. Furthermore, it is expected to prepare the magnetic material with a vertical magnetic structure by either changing the angle between the strong magnetic field and a growth plane of the thin film material, or designing and preparing an asymmetric heterogenous thin film structure thus reducing or counteracting the effect of the demagnetizing field in the vertical direction. The neatly-arranged magnetic moments of the magnetic material generate a strong equivalent magnetic field on the surface of the semiconductor heterogeneous, thereby improving larmor procession of spin electrons, suppressing the dephasing process, and prolonging the spin relaxation time finally.
However, the current room-temperature chamber of the strong magnet is small in size (generally the inner diameter is smaller than 10 cm); and to achieve the fine growth of the magnetic thin film material (requiring multiple evaporation sources and ion sources) and in-situ characterization, multiple components need to be equipped in the chamber, and the system should be multi-functions with complicated structure. Therefore, if the ultrahigh vacuum can be achieved in the room-temperature chamber, the free path of molecules would be increased significantly (an average free path of the molecules can reach tens of meters under the vacuum of 10−4 Pa), so that a multi-growth-beam source can be moved out of the strong magnetic field chamber, and the molecular beam epitaxial growth of the thin film material can be realized. Furthermore, the growth rate, components and crystal structure of the material could be controlled accurately in the atomic scale, so that the technical problems for preparing the high-quality spin semiconductor with sharp interface can be solved. Meanwhile, the in-situ transport characterization of the sample is performed in an ultrahigh vacuum environment with strong magnetic field, so that the influence of various atoms adsorbed on the surface on the spin characteristics can be effectively avoided in the growth and characterization process. Furthermore, the in-situ characterization has the advantages of high sensitivity, good resolution and so on, and the physical mechanism related to the spin can be more intuitively and accurately studied. It is beneficial to better understanding the electron spin quantum characteristics of semiconductors, discover new phenomena, master new rules and propose new control methods.